Generally, when charging a rechargeable battery or a secondary battery, including for example NiCd (Nickel-Cadmium) or NiMH (Nickel-Metal-Hydride), it is known to have a rapid charging process wherein a relatively high constant current is applied to the battery until a certain event occurs. A typical method of detecting this event is to measure the increase in battery temperature as a function of time in order to detect when the battery temperature rate of change (dT/dt or delta_T/delta_t) reaches a predetermined high limit, see for example U.S. Pat. No. 3,852,652 to Jasinski, U.S. Pat. No. 5,329,219 to Garrett, and U.S. Pat. No. 5,550,453 to Bohne et. al.
A common drawback of the above mentioned known charging processes is the use of a constant predetermined reference value to be reached for the measured battery temperature rate of change when terminating the charging process. Use of a predetermined reference value which is constant throughout the battery life sometimes results in undercharge of the battery (leading to a poor battery capacity) or overcharge of the battery (leading to a decreased battery lifetime). Therefore, the need exists for a battery charging method and apparatus that avoid undercharge and overcharge of the battery.
Another drawback of known charging processes in which a characteristic of the battery is monitored for the detecting of an event that indicates the termination of a rapid charging stage, is the appearance of peak values of the characteristic of the battery at the initial stage of charging. To avoid a premature termination of the charging process due to a rise in such a characteristic, the need exists for a battery charging method and apparatus that avoids the detection of the event during the initial charging stage and yet allows the detection of a fully charged battery in order to avoid overcharging of a battery which has already been fully charged.